In order to adjust the posture of the wiring substrate in the inspection apparatus for bringing a plurality of probe pins into uniform and individual contact with the large number of electronic components, the wiring substrate has studs each of which has a bolt and a flat flange having a circular shape in plan view. The flanges of the studs are joined to the back surface of the wiring substrate opposite its front surface having pads for probe for disposing the probe pins, in such a manner that the bolts become perpendicular to the back surface. For example, regarding the case where, on the back surface to which the studs are joined, via conductors (conductors for connection between adjacent layers) are located at positions around the studs, in order for the substrate to be less susceptible to occurrence of cracking in the vicinity of the via conductors even in the event of application of a large external force to the studs, there have been proposed a multilayer ceramic substrate in which a relation is specified for, for example, the distance between the center axis of the via conductor and the circumcircle of a brazing material layer used to join the stud to a surface metal layer formed on the back surface, as well as a method of manufacturing the multilayer ceramic substrate (see, for example, Patent Document 1).
However, the multilayer ceramic substrate and the method of manufacturing the same have the following problem. In the case where a large external force which pulls a stud outward along the axial direction of its bolt is applied to the stud, a shearing force along the thickness direction of the multilayer substrate acts between the peripheral edge of the flat flange of the stud and the back surface of the multilayer ceramic substrate. As a result, a crack along the thickness direction of the substrate may be generated in the ceramic near a region of the back surface of the multilayer substrate, which region is located adjacent to the peripheral edge of the flange of the stud. In the case where such a crack is generated, it becomes difficult to accurately inspect a plurality of electronic components to be inspected, and the multilayer ceramic substrate itself breaks.